Reduction of Gene Expression Noise Caused By Plasmid Copy Number Variation in Mammalian Cells.

In vivo imaging of model organisms is heavily reliant on fluorescent proteins with high brightness. Here we describe a practical method for rapid optimization of fluorescent proteins via directed molecular evolution in mammalian cells. We employed this approach to enhance intracellular brightness of a set of the spectrally diverse fluorescent proteins. The developed proteins demonstrated high performance for fluorescent labeling of neurons in culture and in vivo in model organisms such as C.elegans, Drosophila fruit flies, and zebrafish. The described method has great potential to be adopted by protein engineers due to its simplicity and convenience. We also believe that the new enhanced fluorescent proteins will find wide application for in vivo imaging of small model organisms.